Lyophilized 7 α-hydroxysteroid dehydrogenase: a stable enzyme preparation for routine bile acid analysis

Preparations of 7 alpha-hydroxysteroid dehydrogenase (7 alpha-HSDH) from Escherichia coli strain 23 can be frozen and thawed without significant loss of activity. 7 alpha-HSDH may then be lyophilized into powder form, which is stable for more than 6 months (3% loss of activity). The lyophilized 7 alpha-HSDH preparation has the additional advantage over previously described preparations of a low and stable fluorescence background when applied to the fluorometric estimation of bile acids, especially in combination with thin-layer chromatography. Analysis of duodenal aspirates from 18 normal subjects gave bile acid ratios identical with those reported earlier and obtained by using gas-liquid chromatography. A significant difference in the glycine: taurine ratio between males and females was observed.